Here is a video for 24 volt battery bank charging of the Windtura 750. It shows amps, volts and rpm. http://www.youtube.com/watch?v=SeehUdkgnfo
I will measure them and let you know. We ordered so many pulleys and I cannot remember which ones we actually are using on the set-up in this video. I think the pulley on the engine is much smaller than 3 inches.